There are two major factors that prevent Bitcoin being widely used as a currency. First of all, the transaction fee is not fixed and sometimes it can cost a fortune for the users to make Bitcoin payments (back in 2017 December, the average Bitcoin transaction fee was around $20). When other payment options such as Paypal and Visa charges only a fraction of that, you can't expect a lot many people to use Bitcoin for this purpose. The second factor is the time required to confirm payments. It may take up to 1 hour to confirm Bitcoin payments. For the other modes, it takes less than one minute.
Above these to reasons, volatility is considered. For bitcoin or any other digital asset to serve the purpose of a currency, stability is required. At the moment, bitcoin is looked at as an investment by common people and they intend to improve their financial status with bitcoin. It is just a matter of time before bitcoin becomes a currency. Actually, there are places where bitcoin is used as a medium of exchange.